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Proceedings Paper

Thermal instability of BK7 and how it affects the manufacturing of large high precision surfaces
Author(s): Michael Hyman; Matthew Brunelle; Nohl Schluntz; Michael Gregory; Mark Notargiacomo; Greg Frisch; Jeremiah Triftshauser
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Paper Abstract

When manufacturing precision optical surfaces of relatively larger sizes it is critical to understand the thermal stability of the substrate material. The material properties associated with thermal homogenization are commonly reviewed and soak schedules are created. These schedules ensure a surface under test is in a stable state and is ready for wavefront measurement with an interferometer. However with some materials such as N-BK7, standard soak schedules may not be enough. This paper shows the thermal challenges associated with manufacturing precision optical surfaces when the substrate material is N-BK7, and how the issue can be easily confused with poor metrology. Throughout the manufacturing of precision optical surfaces, the substrates are exposed to varying heat sources and loads. During the manufacturing of lenses greater than 4 inches in diameter we have observed permanent deformation of the optical surface as a result of exposure to temperatures well below the glass strain point. While the reasons why the change occurs is not yet well understood, the result is well documented and was recently observed during the manufacturing of a 15 inch diameter spherical mirror. We use this lens as a case study highlighting the challenges associated with this phenomenon.

Paper Details

Date Published: 16 October 2017
PDF: 6 pages
Proc. SPIE 10448, Optifab 2017, 104481M (16 October 2017); doi: 10.1117/12.2279807
Show Author Affiliations
Michael Hyman, Optimax Systems, Inc. (United States)
Matthew Brunelle, Optimax Systems, Inc. (United States)
Nohl Schluntz, Optimax Systems, Inc. (United States)
Michael Gregory, Optimax Systems, Inc. (United States)
Mark Notargiacomo, Optimax Systems, Inc. (United States)
Greg Frisch, Optimax Systems, Inc. (United States)
Jeremiah Triftshauser, Optimax Systems, Inc. (United States)

Published in SPIE Proceedings Vol. 10448:
Optifab 2017
Julie L. Bentley; Sebastian Stoebenau, Editor(s)

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